Question

The oxide of an element possesses the formula $M_2{O}_3$. If the equivalent weight of the metal is 9, then the atomic weight of the metal will be:

• A. 9
• B. 18
• C. 27
• D. 54

Answer 1

Answer: (C)

27

Let M be the molar mass of the element.

2M g of element combines with $3\times 16=48g$ of oxygen.

$\frac{2M\times 8}{48}=\frac{M}{3}$ g of element combines with $8g$ of oxygen.

The equivalent mass of an element is the mass of the element that combines with 8 g of oxygen.

Thus, the equivalent mass of the element is $\frac{M}{3}$

But it is equal to 9.

Hence, $M=3\times 9=27g/mol$

Hence, the correct option is $\text{C}$